Liquid crystal display with varying thickness

ABSTRACT

A liquid crystal display according to the invention includes a liquid crystal display element ( 100 ) having a liquid crystal layer ( 4 ) containing liquid crystal molecules oriented so as to assume a bend alignment when an image display is being made, and at least one retardation plate for compensating for a retardation of the liquid crystal layer, wherein the display is made by varying the retardation of the liquid crystal layer in accordance with video signals inputted from outside to vary the transmittance of the liquid crystal display element to light for display, characterized in that: the liquid crystal display element ( 100 ) includes a plurality of red pixels for displaying a red color, a plurality of green pixels for displaying a green color, and a plurality of blue pixels for displaying a blue color; and a thickness ( 53 B) of the liquid crystal layer ( 4 ) associated with the blue pixels is larger than a thickness ( 53 R,  53 G) of the liquid crystal layer associated with the red pixels and/or the green pixels.

TECHNICAL FIELD

The present invention relates to liquid crystal displays having suchdisplay capabilities as high-speed response and wide viewing angle and,more particularly, to an optically self-compensated birefringenceembodiment (OCB embodiment) liquid crystal display and a method ofmanufacturing the same.

BACKGROUND ART

In recent years, a great amount of image information is being circulatedwith the progress of multimedia technology. Liquid crystal displays havesprung into wide use as means for displaying such image information.This is because high contrast and wide viewing angle liquid crystaldisplays have been developed and put to practical use by virtue of theprogress of liquid crystal technology. At present, the displaycapability of liquid crystal displays has reached a level comparable tothat of CRT displays.

Liquid crystal displays, however, involve a problem that they are notsuited to motion picture display because the responsiveness thereof isinsufficient for motion picture display. Specifically, though the NTSC(National Television System Committee) system now in force requires thatliquid crystal make a response within one frame period (16.7 msec),existing liquid crystal displays take 100 msec or longer to make aresponse at a portion between adjacent levels of gray in a multi-levelgray scale display. For this reason, there occurs a phenomenon that animage blurs in a motion picture display. Particularly at a portionbetween adjacent levels of gray in a region at which the driving voltageis low, a response is considerably delayed and, hence, a favorablemotion picture display cannot be realized.

In this respect, many attempts have been made to make higher theresponsiveness of liquid crystal displays. Though various liquid crystaldisplay systems for high-speed response have been summarized by Wu etal. (C. S. Wu and S. T. Wu, SPIE, 1665, 250 (1992)), the number of suchsystems expected to have response characteristics required for motionpicture display is limited at present.

Presently, liquid crystal displays comprising an OCB embodiment liquidcrystal display element, a ferroelectric liquid crystal display elementor an antiferroelectric liquid crystal display element are considered tobe promising as liquid crystal displays having such high-speed responseas to be suited for motion picture display.

Among such liquid crystal display elements, ferroelectric liquid crystaldisplay elements and antiferroelectric liquid crystal display elements,which are of a layered structure, involve many problems in terms ofpractical use such as low impact resistance, narrow service temperaturerange, and high temperature dependence of characteristics. For thisreason, attention is actually focused on OCB embodiment liquid crystaldisplay elements using nematic liquid crystal.

In 1983, J. P. Bos demonstrated the high-speed response of such an OCBembodiment liquid crystal display element. Thereafter, OCB embodimentliquid crystal display elements were proved to exhibit both wide viewingangle and high-speed response compatibly with each other if it isprovided with a retardation plate. Since then, research and developmentof such OCB embodiment liquid crystal display elements has becomeactive.

FIG. 24 is a sectional view schematically showing the construction of aconventional OCB embodiment liquid crystal display element. As shown inFIG. 24, the OCB embodiment liquid crystal display element includes aglass substrate 1 formed with a transparent electrode 2 on the undersidethereof, a glass substrate 8 formed with a transparent electrode 7 onthe upper side thereof, and a liquid crystal layer 4 interposed betweenthese glass substrates 1 and 8. An alignment film 3 is formed on theunderside of the transparent electrode 2, while an alignment film 6formed on the upper side of the transparent electrode 7. Liquid crystalmolecules have been filled into a gap between these alignment films 3and 6 to be formed into a liquid crystal layer 4. The alignment layers 3and 6 have been subjected to alignment treatment to align the liquidcrystal molecules in parallel with one another and in the samedirection. The thickness of the liquid crystal layer 4 is maintainedwith spacers 5.

The glass substrate 1 is provided with a sheet polarizer 13 on the upperside thereof, while the glass substrate 8 provided with a sheetpolarizer 16 on the underside thereof, the sheet polarizers 13 and 16being arranged in a cross nicol position. Further, a retardation plate17 is provided between the sheet polarizer 13 and the glass substrate 1,while a retardation plate 18 provided between the sheet polarizer 16 andthe glass substrate 8. A negative retardation plate having ahybrid-aligned primary axis is employed for each of the retardationplates 17 and 18.

The OCB embodiment liquid crystal display element thus constructed ischaracterized in that transition of the alignment condition of liquidcrystal molecules from a splay alignment 4 a to a bend alignment 4 b iscaused by application of a voltage to allow an image to be displayedwith the molecules in the bend alignment condition. Such an OCBembodiment liquid crystal device exhibits considerably improved liquidcrystal responsiveness as compared with TN (Twisted Nematic) embodimentliquid crystal display elements and the like and hence can realize aliquid crystal display suited for motion picture display. Further, theprovision of the retardation plates 17 and 18 makes it possible torealize low-voltage drive and a wide viewing angle.

Meanwhile, the aforementioned OCB embodiment liquid crystal displayelement may be constructed to include color filters for the threeprimary colors (red, green and blue) for realizing a color display.Pixels corresponding to respective color filters for red, green and blueare herein referred to as red pixel(s), green pixel(s) and bluepixel(s), respectively. FIG. 25 is a graph showing wavelength dispersioncharacteristics in accordance with retardations in a normal direction ofliquid crystal layers, respectively, associated with such red pixel,green pixel and blue pixel (hereinafter referred to as normal-directionretardation(s)). FIG. 25 also shows the normal-direction retardation ofa negative retardation plate having a hybrid-aligned primary axis,together with the normal-direction retardations of these liquid crystallayers.

In FIG. 25, reference numerals 81, 82 and 83, respectively, indicatewavelength dispersion characteristics in accordance withnormal-direction retardations of the liquid crystal layers,respectively, associated with the red pixel, green pixel and blue pixel.Reference numeral 84 indicates the wavelength dispersion characteristicin accordance with normal-direction retardations of the aforementionednegative retardation plate.

As shown in FIG. 25, the normal-direction retardation of the liquidcrystal layer associated with the red pixel generally conforms to thatof the negative retardation plate in a wavelength region correspondingto red (in the vicinity of 650 nm). Likewise, the normal-directionretardation of the liquid crystal layer associated with the green pixelgenerally conforms to that of the negative retardation plate in awavelength region corresponding to blue (in the vicinity of 550 nm).However, the normal-direction retardation of the liquid crystal layerassociated with the blue pixel does not conform to that of the negativeretardation plate in a wavelength region corresponding to blue (in thevicinity of 450 nm). Thus, there arises a problem that when the OCBembodiment liquid crystal display element makes a black display, thedisplay becomes bluish.

DISCLOSURE OF INVENTION

The present invention has been made in view of the foregoingcircumstances and intends to provide an OCB embodiment liquid crystaldisplay element capable of making a favorable black display bydecreasing bluishness when a black display is made, a liquid crystaldisplay including the OCB embodiment liquid crystal display element, anda method of manufacturing the liquid crystal display element.

With a view to attaining these objects, the present invention provides aliquid crystal display comprising a liquid crystal display elementhaving a liquid crystal layer containing liquid crystal moleculesoriented so as to assume a bend alignment when an image display is beingmade, and at least one retardation plate for compensating for aretardation of the liquid crystal layer, wherein the display is made byvarying the retardation of the liquid crystal layers in accordance withvideo signals inputted from outside to vary the transmittance of theliquid crystal display element to light for display, characterized inthat: the liquid crystal display element includes a plurality of redpixels for displaying a red color, a plurality of green pixels fordisplaying a green color, and a plurality of blue pixels for displayinga blue color; and a thickness of the liquid crystal layer associatedwith the blue pixels is larger than a thickness of the liquid crystallayer associated with the red pixels and/or the green pixels.

With such a construction, the retardation of the liquid crystal layerassociated with the blue pixels and that of the retardation platesubstantially conform to each other in a wavelength region correspondingto blue. Thus, it is possible to decrease bluishness that occurs when ablack display is made. Accordingly, a favorable black display can berealized.

In this case, a difference between the thickness of the liquid crystallayer associated with the blue pixels and thickness of the liquidcrystal layer associated with the red pixels and/or the green pixels maybe not less than 0.2 μm and not more than 1.0 μm. Alternatively, thethickness of the liquid crystal layer associated with the blue pixelsmay be not less than 104% and not more than 120% of the thickness of theliquid crystal layer associated with the red pixels and/or the greenpixels.

By thus adjusting the thickness of the liquid crystal layer associatedwith the blue pixels to a suitable value, it is possible to decreasebluishness in a black display sufficiently.

The liquid crystal display according to the present invention mayfurther comprise a lighting device having light sources for emitting ared light, a green light and a blue light, respectively, and lightingdevice control means for controlling the lighting device in a manner tocause the light sources to emit respective color lights by timedivision. This arrangement allows even a so-called field sequentialcolor system to realize a favorable black display.

According to the present invention, there is provided a liquid crystaldisplay comprising a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, wherein the display is made by varying theretardation of the liquid crystal layer in accordance with video signalsinputted from outside to vary the transmittance of the liquid crystaldisplay element to light for display, characterized in that: the liquidcrystal display element includes a plurality of red pixels fordisplaying a red color, a plurality of green pixels for displaying agreen color, and a plurality of blue pixels for displaying a blue color;and an alignment direction of the liquid crystal molecules associatedwith the blue pixels is different from an alignment direction of theliquid crystal molecules associated with the red pixels and/or the greenpixels.

Such a construction makes it possible to control thevoltage-transmittance characteristic associated with the blue pixels. Asa result, it is possible to decrease the bluishness that occurs when ablack display is made.

In this case, the alignment direction of the liquid crystal moleculesassociated with the blue pixels may form an angle of not less than 2degrees and not more than 30 degrees with respect to the alignmentdirection of the liquid crystal molecules associated with the red pixelsand/or the green pixels. This feature makes it possible to decreasebluishness that occurs when a black display is made without loweringdisplay characteristics including a viewing angle characteristic and aluminance.

The liquid crystal display according to the present invention mayfurther comprise a lighting device having light sources for emitting ared light, a green light and a blue light, respectively, and lightingdevice control means for controlling the lighting device in a manner tocause the light sources to emit respective color lights by timedivision. This arrangement allows even a so-called field sequentialcolor system to realize a favorable black display.

According to the present invention, there is provided a liquid crystaldisplay comprising a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, wherein the display is made by varying theretardation of the liquid crystal layer in accordance with video signalsinputted from outside to vary the transmittance of the liquid crystaldisplay element to light for display, characterized in that: the liquidcrystal display element includes a plurality of red pixels fordisplaying a red color, a plurality of green pixels for displaying agreen color, and a plurality of blue pixels for displaying a blue color;and a pretilt angle of the liquid crystal molecules associated with theblue pixels is different from each of pretilt angles of the liquidcrystal molecules associated with the red pixels and the green pixels,while the pretilt angle of the liquid crystal molecules associated withthe red pixels is substantially equal to the pretilt angle of the liquidcrystal molecules associated with the green pixels.

Such a construction makes it possible to control thevoltage-transmittance characteristic associated with the blue pixels. Asa result, it is possible to decrease the bluishness that occurs when ablack display is made.

In this case, the pretilt angle of the liquid crystal moleculesassociated with the blue pixels may be smaller than each of the pretiltangles of the liquid crystal molecules associated with the red pixelsand the green pixels. Alternatively, the pretilt angle of the liquidcrystal molecules associated with the blue pixels may be not less than5% and not more than 50% of each of the pretilt angles of the liquidcrystal molecules associated with the red pixels and the green pixels.

The liquid crystal display according to the present invention mayfurther comprise a lighting device having light sources for emitting ared light, a green light and a blue light, respectively, and lightingdevice control means for controlling the lighting device in a manner tocause the light sources to emit respective color lights by timedivision. This arrangement allows even a so-called field sequentialcolor system to realize a favorable black display.

According to the present invention, there is provided a liquid crystaldisplay comprising a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, wherein the display is made by varying theretardation of the liquid crystal layer in accordance with video signalsinputted from outside to vary the transmittance of the liquid crystaldisplay element to light for display, characterized in that the liquidcrystal molecules have an refractive index anisotropy of 0.15 or more,while the product of the refractive index anisotropy and the thicknessof the liquid crystal layer is 0.80 μm or less.

According to the present invention, there is provided a liquid crystaldisplay comprising a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, wherein the display is made by varying theretardation of the liquid crystal layer in accordance with video signalsinputted from outside to vary the transmittance of the liquid crystaldisplay element to light for display, characterized in that: the liquidcrystal display element has a negative uniaxial retardation platecomprising a triacetylcellulose film; and the triacetylcellulose filmhas refractive indexes along three axes thereof, any one of therefractive indexes being not less than 1.45 and not more than 1.50.

In this case, the negative uniaxial retardation plate may furthercomprise a discotic liquid crystal film. This feature makes it possibleto control the wavelength dispersion characteristic of the negativeuniaxial retardation plate easily and hence to approximate it to thewavelength dispersion characteristic of the liquid crystal layer. As aresult, it is possible to decrease bluishness when a black display ismade.

According to the present invention, there is provided a liquid crystaldisplay comprising a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is made, and at least oneretardation plate for compensating for a retardation of the liquidcrystal layer, wherein the display is made by varying the retardation ofthe liquid crystal layer in accordance with video signals inputted fromoutside to vary the transmittance of the liquid crystal display elementto light for display, characterized in that: the liquid crystal displayelement has a biaxial retardation plate comprising a triacetylcellulosefilm; and the triacetylcellulose film has refractive indexes along threeaxes thereof, any one of the refractive indexes being not less than 1.45and not more than 1.50.

With such a construction, it is possible to inhibit leakage of obliquelyincident light when a black display is made without the necessity ofproviding a positive uniaxial retardation plate as well as to decreasebluishness of the black display.

According to the present invention, there is provided a liquid crystaldisplay comprising: a liquid crystal display element having a liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer; and a lighting device for emitting light outgoingto the liquid crystal display element, wherein the display is made byvarying the retardation of the liquid crystal layer in accordance withvideo signals inputted from outside to vary the transmittance of theliquid crystal display element to the light outgoing from the lightingdevice for display, characterized in that: the liquid crystal displayelement includes a plurality of red pixels for displaying a red color, aplurality of green pixels for displaying a green color, and a pluralityof blue pixels for displaying a blue color; and the lighting device isconfigured to substantially equalize outgoing light amounts inrespective wavelength regions corresponding to red, green and blue.

In this case, the lighting device may have a light source for emittingthe outgoing light, and a filter for filtering the outgoing lightemitted from the light source in a manner that the half width of aspectrum of the outgoing light in the wavelength region corresponding toblue is 30 nm or less.

In the liquid crystal display according to the foregoing invention, anarrangement is possible such that the lighting device has light sourcesfor emitting a red light, a green light and a blue light, respectively,and that the liquid crystal display further comprises lighting devicecontrol means for controlling the lighting device in a manner to causethe light sources to emit respective color lights by time division. Thisarrangement allows even a so-called field sequential color system torealize a favorable black display.

In the liquid crystal display according to the foregoing invention, thelighting device may have a light-emitting diode for emitting theoutgoing light, or otherwise the lighting device may have anelectroluminescent device for emitting the outgoing light.

According to the present invention, there is provided a method ofmanufacturing a liquid crystal display including a liquid crystaldisplay element having a liquid crystal cell comprising a liquid crystallayer sandwiched between a pair of opposed substrates, the liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, the liquid crystal cell having a plurality of redpixels for displaying a red color, a plurality of green pixels fordisplaying a green color and a plurality of blue pixels for displaying ablue color, wherein the display is made by varying the retardation ofthe liquid crystal layer in accordance with video signals inputted fromoutside to vary the transmittance of the liquid crystal display elementto light outgoing from the lighting device for display, characterized bycomprising the steps of: forming a photosensitive photoresist filmhaving a predetermined thickness on an inwardly oriented face of one ofthe pair of substrates; etching the photosensitive photoresist film thusformed in regions corresponding to the blue pixels so that the thicknessof said one of the substrates in the regions corresponding to the bluepixels has a smaller thickness than the thickness of said one of thesubstrates in regions corresponding to the red pixels and/or the greenpixels; and bonding said one of the substrates thus etched and the othersubstrate to each other in an opposed fashion to allow the liquidcrystal layer to be formed so that a thickness of the liquid crystallayer associated with the blue pixels becomes larger than a thickness ofthe liquid crystal layer associated with the red pixels and/or the greenpixels.

This method enables easy manufacture of a liquid crystal display whereina thickness of a liquid crystal layer associated with blue pixels islarger than a thickness of the liquid crystal layer associated with thered pixels and/or the green pixels.

In this case, the predetermined thickness may be not less than 0.2 μmand not more than 1.0 μm. By so setting, it is possible to easilymanufacture a liquid crystal display wherein a thickness of a liquidcrystal layer associated with blue pixels is larger by not less than 0.2μm and not more than 1.0 μm than a thickness of the liquid crystal layerassociated with the red pixels and/or the green pixels.

According to the present invention, there is provided a method ofmanufacturing a liquid crystal display including a liquid crystaldisplay element having a liquid crystal cell comprising a liquid crystallayer sandwiched between a pair of opposed substrates, the liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when an image display is being made, and atleast one retardation plate for compensating for a retardation of theliquid crystal layer, the liquid crystal cell having a plurality of redpixels for displaying a red color, a plurality of green pixels fordisplaying a green color and a plurality of blue pixels for displaying ablue color, wherein the display is made by varying the retardation ofthe liquid crystal layer in accordance with video signals inputted fromoutside to vary the transmittance of the liquid crystal display elementto light outgoing from the lighting device for display, characterized bycomprising the steps of: forming a photosensitive alignment film on aninwardly oriented face of each of the pair of substrates; and subjectingthe alignment film to an alignment treatment by irradiating thealignment film with linearly polarized light, wherein at the step of thealignment treatment, the photosensitive alignment film in regionscorresponding to the blue pixels are irradiated with linearly polarizedlight having a different polarization direction from that of linearlypolarized light with which the photosensitive alignment film in regionscorresponding to the red pixels and/or the green pixels is irradiated,whereby an alignment direction of the liquid crystal moleculesassociated with the blue pixels becomes different from an alignmentdirection of the liquid crystal molecules associated with the red pixelsand/or the green pixels.

According to the present invention, there is further provided a methodof manufacturing a liquid crystal display including a liquid crystaldisplay element having a liquid crystal cell comprising a liquid crystallayer sandwiched between a pair of opposed substrates, the liquidcrystal layer containing liquid crystal molecules oriented so as toassume a bend alignment when image display is being made, and at leastone retardation plate for compensating for a retardation of the liquidcrystal layer, the liquid crystal cell having a plurality of red pixelsfor displaying a red color, a plurality of green pixels for displaying agreen color and a plurality of blue pixels for displaying a blue color,wherein the display is made by varying the retardation of the liquidcrystal layer in accordance with video signals inputted from outside tovary the transmittance of the liquid crystal display element to lightoutgoing from the lighting device for display, characterized bycomprising the steps of: forming an alignment film on an inwardlyoriented face of each of the pair of substrates; rubbing the alignmentfilm thus formed; and irradiating the alignment film with light whilevarying the amount of the light before or after the rubbing step so thata pretilt angle of the liquid crystal molecules associated with the bluepixels becomes different from each of pretilt angles of the liquidcrystal molecules associated with the red pixels and the green pixels.

The foregoing and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof the preferred embodiments of the present invention when read withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view schematically showing the construction of aliquid crystal display element included in a liquid crystal displayaccording to embodiment 1 for carrying out the present invention.

FIG. 2 includes views schematically showing the arrangement of a liquidcrystal cell included in the liquid crystal display element of theliquid crystal display according to embodiment 1; specifically, FIG. 2(a) is a sectional view of the liquid crystal cell, while FIG. 2( b) isan enlarged view of a liquid crystal layer portion in the sectionalview.

FIG. 3 is a plan view of the liquid crystal display element included inthe liquid crystal display according to embodiment 1 for indicating thedirections in which optical devices included in the liquid crystaldisplay element are disposed.

FIG. 4 is a view illustrating the process of forming a dented structuralbody included in the liquid crystal display element of the liquidcrystal display according to embodiment 1.

FIG. 5 is a plan view showing a photo mask used in the formation ofdented portions.

FIG. 6 is a view illustrating the process of forming dented portionsincluded in the liquid crystal display element of the liquid crystaldisplay according to embodiment 1.

FIG. 7 is a block diagram illustrating the configuration of the liquidcrystal display according to embodiment 1.

FIG. 8 is a graph showing voltage-luminance characteristics at redpixel, green pixel and blue pixel of the liquid crystal displayaccording to embodiment 1.

FIG. 9 is a graph showing the spectral distribution of transmitted lightnormal to a liquid crystal display according to example 1 of embodiment1 when a black display is made.

FIG. 10 is a sectional view schematically showing the outline of anotherarrangement of the liquid crystal display according to embodiment 1.

FIG. 11 is a graph showing the spectral distribution of transmittedlight normal to a liquid crystal display according to a comparativeexample.

FIG. 12 is a sectional view schematically showing the arrangement of aliquid crystal cell included in a liquid crystal display element of aliquid crystal display according to embodiment 2 for carrying out thepresent invention.

FIG. 13 is an explanatory view indicating polarization directions ofultraviolet light applied to regions corresponding to red pixel, greenpixel and blue pixel, respectively in the liquid crystal display elementincluded in the liquid crystal display according to embodiment 2.

FIG. 14 is an explanatory view indicating a rubbing direction in whichan alignment film provided in a liquid crystal display element includedin a liquid crystal display according to embodiment 3 for carrying outthe present invention is rubbed.

FIG. 15 is a graph for comparison between wavelength dispersioncharacteristics in accordance with retardations of liquid crystal layersusing respective liquid crystal materials that are different inrefractive index anisotropy Δn.

FIG. 16 is a diagram showing the relation between the combination ofrefractive index anisotropy Δn of a liquid crystal material andretardation Δnd and the bluishness that occurs when a black display ismade.

FIG. 17 is a graph showing the wavelength dispersion characteristics ofrespective optical elements included in a liquid crystal displayelement.

FIG. 18 is a sectional view schematically showing the construction of aliquid crystal display element included in a liquid crystal displayaccording to embodiment 5 for carrying out the present invention.

FIG. 19 is a sectional view schematically showing the outline of anexemplary arrangement of the liquid crystal display according toembodiment 6 for carrying out the present invention.

FIG. 20 includes graphs each showing the spectrum of light outgoing froma light source 151 included in the liquid crystal display according toembodiment 6; specifically, FIGS. 20( a) and 20(b) are graphs showingspectra obtained with and without the provision of an interferencefilter 152, respectively.

FIG. 21 is a sectional view schematically showing the outline of anotherarrangement of the liquid crystal display according to embodiment 6.

FIG. 22 is a graph showing the spectrum of an LED as a light sourceincluded in a backlight of the liquid crystal display according toembodiment 6.

FIG. 23 is a graph showing the spectrum of an EL as a light sourceincluded in a backlight of the liquid crystal display according toembodiment 6.

FIG. 24 is a sectional view schematically showing the construction of aconventional OCB embodiment liquid crystal display element.

FIG. 25 is a graph showing wavelength dispersion characteristics inaccordance with retardations in a normal direction of a liquid crystallayer at red pixel, green pixel and blue pixel included in theconventional OCB embodiment liquid crystal display.

BEST EMBODIMENT FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments for carrying out the present invention will bedescribed in detail with reference to the drawings. It should be notedthat in the following embodiments the color coordinates of a display inthe direction normal to a liquid crystal display element are measuredwhen the liquid crystal display element is making a black display. Inthis case the display becomes the best achromatic display with nocoloring when the color coordinates assume substantially (0.3, 0.3).Therefore, the present invention intends to approximate the colorcoordinates to (0.3, 0.3) in order to realize a favorable black display.

Embodiment 1

According to embodiment 1 for carrying out the present invention, thereis provided a liquid crystal display wherein a thickness of a liquidcrystal layer associated with blue pixels for a blue display is madelarger than each of thicknesses of the liquid crystal layer associatedwith red pixels for a red display and green pixels for a green display,thereby decreasing bluishness of a black display.

EXAMPLE 1

FIG. 1 is a sectional view schematically showing the construction of aliquid crystal display element included in a liquid crystal displayaccording to example 1 of embodiment 1 for carrying out the presentinvention. For convenience, the X direction in the figure indicates anascending direction of the liquid crystal display element.

As shown in FIG. 1, the liquid crystal display element 100 included inthe liquid crystal display according to example 1 has a liquid crystalcell 101 to be described later. On the upper side of the liquid crystalcell 101 are sequentially stacked a retardation film 14 a comprising anoptical medium having a hybrid-aligned primary axis and a negativerefractive index anisotropy (hereinafter referred to as “negativeretardation film” simply”), a negative uniaxial retardation film 12 a, apositive uniaxial retardation film 15, and an analyzer 13. On theunderside of the liquid crystal cell 101 are sequentially stacked anegative retardation film 14 b, a negative uniaxial retardation film 12b, and a polarizer 16.

FIG. 2 includes views each schematically showing the arrangement of theaforementioned liquid crystal cell 101; specifically, FIG. 2( a) is asectional view of the liquid crystal cell 101, while FIG. 2( b) is anenlarged view of a liquid crystal layer portion in the sectional view.As shown in FIG. 2( a), the liquid crystal cell 101 includes a pair ofsubstrates, that is, an upper substrate 102 and a lower substrate 103.The upper substrate 102 and the lower substrate 103 are disposed to faceeach other through spacers (not shown), and a liquid crystal layer 4 isdisposed in the clearance defined between the upper substrate 102 andthe lower substrate 103. Into the liquid crystal layer 4 are injectedliquid crystal molecules 201, which assume a bend alignment as shown inFIG. 2( b) when an image display is being made.

The upper substrate 102 comprises a transparent electrode 2 and analignment film 3 which are formed and stacked sequentially on theunderside of a glass substrate 1. Between the glass substrate 1 and thetransparent electrode 2 are formed red color filters 51R, green colorfilters 51G and blue color filters 51B. A light-shielding film 52 calleda black matrix is disposed at the boundary between adjacent colorfilters of respective colors. Hereinafter, pixels corresponding to redcolor filter 51R, green color filter 51G and blue color filter 51B willbe referred to as red pixel, green pixel and blue pixel, respectively.

The lower substrate 103, on the other hand, comprises a transparentelectrode 7 and an alignment film 6 which are formed and stackedsequentially on the upper side of a glass substrate 8. The lowersubstrate 103 has dented portions 10 at locations corresponding to bluepixels. Reference numeral 20 denotes a resist thin film to be describedlater.

FIG. 3 is a plan view of the liquid crystal display element 100 forindicating the directions in which optical devices included in theliquid crystal display element 100 are disposed. Referring to FIG. 3 aswell as FIG. 1, arrows 17 and 18 indicate the directions of alignmenttreatments done on the upper substrate 102 and the lower substrate 103,respectively. Arrows 26 and 27, respectively, indicate the primary axialdirections of the negative retardation films 14 a and 14 b. As shown inFIG. 3, the negative retardation films 14 a and 14 b are disposed sothat their respective primary axial directions 26 and 27 conform to thealignment treatment directions 17 and 18.

Arrow 19 in FIG. 3 indicates the slow axis of the positive uniaxialretardation film 15. As shown in FIG. 3, the positive uniaxialretardation film 15 is disposed so that its slow axis 19 forms an angleof 45 degrees with respect to the alignment treatment directions 17 and18.

Further, arrows 24 and 25 in FIG. 3 indicate the transmission axes ofthe polarizer 16 and the analyzer 13, respectively. As shown in FIG. 3,the polarizer 16 is disposed so that its transmission axis 24 extends inthe same direction as the slow axis 19 of the positive uniaxialretardation film 15. On the other hand, the polarizer 13 is disposed sothat its transmission axis 25 perpendicularly intersects thetransmission axis 24 of the polarizer 16.

In this example, the aforementioned liquid crystal display element 100was manufactured as follows. FIG. 4 is a view illustrating the processof forming the aforementioned dented portions 10. First, a polycarbonate(PC) type resist material produced by JSR Co., Ltd. was applied onto theupper side of the glass substrate 8 to form the resist thin film 20having a thickness of 0.5 μm. Subsequently, a photo mask 21 having aplurality of openings 22 in rectangular patterns as shown in FIG. 5 wassuperposed on the resist thin film 20, and the resulting structure wasexposed to parallel ultraviolet rays 23 by irradiation. The resist thinfilm 20 thus exposed was developed, rinsed and then prebaked at 90° C.to form the dented portions 10 as shown in FIG. 6.

The aforementioned openings 22 of the photo mask 21 are positionedcorresponding to the locations of the blue pixels. Accordingly, theaforementioned dented portions 10 are formed corresponding to the bluepixels.

After the plurality of dented portions 10 had been thus formed, thetransparent electrode 7 having a thickness of 2000 Å was formed by aknown technique. Subsequently, the underside of the transparentelectrode 2 and the upper side of the transparent electrode 7 werecoated with an alignment film-forming coating material SE-7492 producedby NISSAN CHEMICAL INDUSTRIES, LTD. by a spin coating process, which inturn was baked at 180° C. for one hour and then cured to form thealignment films 3 and 6.

The alignment films 3 and 6 thus formed were rubbed in respectivealignment treatment directions 17 and 18 indicated in FIG. 3.Subsequently, the upper substrate 102 and the lower substrate 102 werebonded to each other so that a spacing therebetween associated with thered pixels and green pixels, that is, a thickness of liquid crystallayer 4 (indicated at 53R and 53G in FIG. 2), assumed 5.2 μm with use ofspacers produced by SEKISUI FINE CHEMICAL Co., Ltd. and a sealing resinnamed STRUCT BOND 352A produced by MITSUI TOUATSU KAGAKU Co., Ltd. Inthis case, a thickness (indicated at 53B in FIG. 2) of liquid crystallayer 4 associated with the blue pixels assumed 5.7 μm, which is the sumof 5.2 μm noted above and 0.5 μm as the thickness of the dented portions10. Thereafter, a liquid crystal MT-5583 (refractive index anisotropyΔn=0.140) was injected into the liquid crystal layer 4 by a vacuuminjection process to complete the liquid crystal cell 101.

Though the thicknesses 53R and 53G of liquid crystal layer 4 associatedwith the red pixels and the green pixels were adjusted to 5.2 μm in thisexample, the present invention is not limited to this feature. However,if the difference between the thicknesses 53R and 53G of liquid crystallayer 4 associated with the red pixels and the green pixels and thethickness 53B of liquid crystal layer 4 associated with the blue pixelsis too small, the retardation of liquid crystal layer 4 at the bluepixels cannot become sufficiently large. On the other hand, if thedifference in thickness is too large, the retardation of liquid crystallayer 4 at the blue pixels becomes so large that a favorable displaycannot be obtained. For this reason, the difference in thickness isdesirably not less than about 0.2 μm and not more than about 1.0 μm.Stated otherwise, the difference in thickness is desirably not less thanabout 4% and not more than about 20% of each of the thicknesses 53R and53G of liquid crystal layer 4 associated with the red pixels and thegreen pixels. That is, the thickness 53B of liquid crystal layer 4associated with the blue pixels is desirably not less than about 104%and not more than about 120% of each of the thicknesses 53R and 53G ofliquid crystal layer 4 associated with the red pixels and the greenpixels.

On the upper side of the liquid crystal cell 101 thus fabricated weresequentially stacked the negative retardation film 14 a, negativeuniaxial retardation film 12 a, positive uniaxial retardation film 15and analyzer 13, and on the underside of the liquid crystal cell 101were sequentially stacked the negative retardation film 14 a, negativeuniaxial retardation film 12 b and polarizer 16, whereby the liquidcrystal display element 100 was completed.

Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 36 nm, which was found from the following formula (1),and retardation Re in the plane of the positive uniaxial retardationfilm 15 was 150 nm, which was found in the same manner. Similarly,retardation Rth in the thicknesswise direction of each of the negativeuniaxial retardation films 12 a and 12 b was 175 nm.Re=(nx−ny)×d  (1)Rth=((nx+ny)/2−nz)×d  (2)wherein nx and ny each represent a refractive index in a plane, nzrepresents a refractive index in a thicknesswise direction, and drepresents the thickness of a film.

In this example, retardation Δnd of liquid crystal layer 4 defined bythe product of thickness d of liquid crystal layer 4 and refractiveindex anisotropy Δn of liquid crystal molecules 201 was set to 0.73 μm.

FIG. 7 is a block diagram showing the configuration of the liquidcrystal display including the liquid crystal display element 100manufactured as above. In FIG. 7, the liquid crystal display 1 is of theTFT (Thin Film Transistor) type comprising the aforementioned liquidcrystal display element 100, blocks 32, 33 and 34, and a backlight (notshown) for emitting white light. Referring to FIG. 7 as well as FIG. 2,the lower substrate 103 serves as a TFT substrate. In the TFT substrate,Gate lines 36 and source lines 37 are formed in a matrix pattern, andpixels delimited by these gate lines 36 and source lines 37 are eachformed with a pixel electrode 39 and a switching element 38. The liquidcrystal display is constructed to drive the gate lines 36 and the sourcelines 37 by means of a gate driver 33 and a source driver 34,respectively and to control the gate driver 33 and the source driver 34by means of a controller 22.

In the liquid crystal display 1 thus constructed, the controller 22outputs control signals to the gate driver 33 and the source driver 34in response to an video signal 35 inputted from outside. In this case,the gate driver 33 outputs a gate signal to the gate lines 36 to turn ONthe switching elements 38 of respective pixels sequentially, while thesource driver 34 inputs the video signal to the pixel electrodes 39 ofrespective pixels through the source lines 37 timely with the switching.This causes liquid crystal molecules 201 to be modulated, so that thetransmittance thereof to light outgoing from the backlight varies toallow the user watching the liquid crystal display 1 to view an imagecorresponding to the video signal 35.

FIG. 8 is a graph showing voltage-luminance characteristics at redpixel, green pixel and blue pixel of the liquid crystal display element100 obtained when an image display is made using the aforementionedliquid crystal display 1. As shown in FIG. 8, the luminance of the bluepixel assumes its lowest value when the applied voltage is 7.2 V, whilethe luminance of each of the red pixel and the green pixel assumes itslowest value when the applied voltage is 7.1 V. It is to be noted thatthe voltage required for a white display is determined from a voltage atwhich the bend alignment inversely transits to the splay alignment. Inthe case of the liquid crystal display element 100 according to thisexample, the voltage at which such inverse transition occurred at allthe red, green and blue pixels was 2.2 V.

FIG. 9 is a graph showing the spectral distribution of transmitted lightnormal to the liquid crystal display element 100 making a black display.In this case the color coordinates were (0.3120, 0.3227). Since the bestachromatic display with no coloring results when the color coordinatesare close to about (0.3, 0.3) as described above, it can be understoodthat this example could realize a favorable black display.

Though retardation Δnd is set to 0.73 μm in this example, it is needlessto say that retardation Δnd is not limited to this value.

Variation 1

Next, a variation of this embodiment will be described. The liquidcrystal display according to example 1 is adapted to realize a colordisplay by means of the color filter system. In contrast, a liquidcrystal display according to variation 1 is adapted to make a colordisplay by means of the field sequential color system.

FIG. 10 is a sectional view schematically showing the outline of anarrangement of the liquid crystal display according to variation 1. Asshown in FIG. 10, liquid crystal display element 100 included in theliquid crystal display according to variation 1 is of the samearrangement as liquid crystal display element 100 according to example 1except that the color filters 51R, 51G and 51B of the three colors arenot provided. For this reason, FIG. 10 shows only the arrangement ofliquid crystal cell 101 included in the liquid crystal display element100 of the liquid crystal display according to variation 1 and uses likereference numerals as used in example 1.

The liquid crystal display including such a liquid crystal displayelement 100 is of the TFT type like example 1 but is different fromexample 1 in that backlight 150 comprising light-emitting diodes(hereinafter referred to as LEDs) for emitting lights of three colorsthat are spread all over the backlight with predetermined intervals isprovided below the liquid crystal display element 100. Here, the liquidcrystal display element 100 and the backlight 150 are disposed so thatred pixels, green pixels and blue pixels of the liquid crystal displayelement 100 correspond to red LEDs 151R, green LEDs 151G and blue LEDs151B of the backlight 150. The LEDs of respective colors included in thebacklight 150 emit a red light, a green light and a blue light in thisorder by time division to realize a color display.

Like the liquid crystal display of example 1, the liquid crystal displaythus arranged was capable of making a black display with decreasedbluishness. As a result, a favorable black display could be realized.

Comparative Example 1

In a liquid crystal display element included in a liquid crystal displayaccording to comparative example 1, thicknesses of a liquid crystallayer corresponding to red pixel, green pixel and blue pixel are equalto each other. Since other features are similar to correspondingfeatures of the liquid crystal display element 100 according to example1, description thereof is omitted.

An image display was made using the liquid crystal display according tocomparative example 1, and voltage-luminance characteristics at redpixel, green pixel and blue pixel of the liquid crystal display elementwere determined in the same manner as in example 1. As a result, theluminance of the blue pixel assumed its lowest value when the appliedvoltage was 6.7 V, while the luminance of each of the red pixel and thegreen pixel assumed its lowest value when the applied voltage was 7.1 V.

FIG. 11 is a graph showing the spectral distribution of transmittedlight normal to the liquid crystal display according to comparativeexample 1. The color coordinates in this case assume (0.2035, 0.1607)and, hence, it can be seen therefrom that a black display is tintedblue.

Embodiment 2

According to embodiment 2 for carrying out the present invention, thereis provided a liquid crystal display wherein the alignment direction ofliquid crystal molecules at blue pixels for a blue display is shifted bya predetermined angle from the alignment direction of liquid crystalmolecules at red pixels and green pixels, respectively, for a reddisplay and a green display, thereby decreasing bluishness when a blackdisplay is made.

EXAMPLE 2

FIG. 12 is a sectional view schematically showing the arrangement of aliquid crystal cell included in a liquid crystal display element of aliquid crystal display according to embodiment 2 for carrying out thepresent invention. As shown in FIG. 12, the liquid crystal cell 101 haslower substrate 103 with no dented portion, and thicknesses of liquidcrystal layer at red, green and blue pixels are equal to each other,unlike the liquid crystal cell in example 1. Since other features aresimilar to corresponding features of the liquid crystal cell 101 inexample 1, description thereof is omitted by the use of like referencenumerals. Also, other features than the liquid crystal cell 101 aresimilar to corresponding features of the liquid crystal displayaccording to example 1 having been described with reference to FIG. 1and, hence, description thereof is omitted.

Hereinafter, the process for manufacturing the liquid crystal displayelement 100 included in the liquid crystal display according to example2 will be described with reference to FIGS. 1 and 12. First, theunderside of transparent electrode 2 and the upper side of transparentelectrode 7 were each coated with a polyimide alignment film-formingcoating material LPP-JP265CP (solvent: cyclopentanone) produced by RolicCo. by a spin coating process, which in turn was baked at 150° C. forone hour and then cured to form alignment films 3 and 6.

The alignment films 3 and 6 thus formed were irradiated with linearlypolarized ultraviolet light obliquely at an angle of 30 degrees withrespect to the direction normal to the substrate (radiation energy onthe substrate was 0.50 J/cm²) for 10 minutes. FIG. 13 is an explanatoryview indicating polarization directions of the ultraviolet light appliedto regions, respectively, corresponding to red pixel, green pixel andblue pixel. As shown in FIG. 13, polarization direction 56R ofultraviolet light applied to region 55R of each alignment film 3, 6corresponding to the red pixel is the same as polarization direction 56Gof ultraviolet light applied to region 55G corresponding to the greenpixel. On the other hand, polarization direction 56B of ultravioletlight applied to region 55B of each alignment film 3, 6 corresponding tothe blue pixel forms an angle of 5 degrees with respect to each of thepolarization directions 56R and 56G. Therefore, the alignment directionof liquid crystal molecules 201 associated with the blue pixel isdifferent by 5 degrees from each of the alignment directions of liquidcrystal molecules 201 associated with the red pixel and green pixel.

Bluishness of a black display decreases as the alignment direction ofliquid crystal molecules 201 associated with the blue pixel approximatesto the transmission axis of sheet polarizer 16. However, displaycharacteristics including viewing angle characteristic and luminancebecome lower. For this reason, the angle formed between the polarizationdirection 56R,56G and the polarization direction 56B, that is, the angleformed between each of the alignment directions of liquid crystalmolecules 201 associated with the red pixel and green pixel and thealignment direction of liquid crystal molecules associated with the bluepixel, is suitably not less than about 2 degrees and not more than about30 degrees, preferably not less than about 5 degrees and not more thanabout 10 degrees.

Subsequently, upper substrate 102 and lower substrate 103 were bonded toeach other so that the spacing therebetween, that is, the thickness ofliquid crystal layer 4, assumed 5.8 μm with use of spacers (not shown)produced by SEKISUT FINE CHEMICAL Co., Ltd. and a sealing resin namedSTRUCT BOND 352A produced by MITSUI TOUATSU KAGAKU Co., Ltd. Thereafter,a liquid crystal MT-5583 (refractive index anisotropy Δn=0.140) wasinjected into the liquid crystal layer 4 by a vacuum injection processto complete the liquid crystal cell 101. The pretilt angle of liquidcrystal molecules at the interface with each of the alignment films 3and 6 was about 2 degrees.

As shown in FIG. 1, on the upper side of the liquid crystal cell 101thus fabricated were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 a, positive uniaxialretardation film 15 and analyzer 13, and on the underside of the liquidcrystal cell 101 were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 b and polarizer 16, whereby theliquid crystal display element 100 according to example 2 was completed.

The aforementioned optical elements were disposed as shown in FIG. 3. Itshould be noted that alignment treatment directions 17 and 18 in FIG. 3represent alignment treatment directions in regions corresponding to redpixels and green pixels. Alignment treatment direction in regionscorresponding to blue pixels was as described above with reference toFIG. 13.

Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 39 nm, which was found from the formula (1) noted above,and retardation Re in the plane of the positive uniaxial retardationfilm 15 was 150 nm, which was found in the same manner. Similarly,retardations Rth in the thicknesswise direction of each of the negativeuniaxial retardation films 12 a and 12 b were 220 nm.

In this example, the retardation Δnd of the liquid crystal layer 4defined by the product of the thickness d of the liquid crystal layer 4and the refractive index anisotropy Δn of liquid crystal molecules 201was set to 0.81 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the liquid crystal display element 100thus manufactured. As a result, the luminance of the blue pixel assumedits lowest value when the applied voltage was 6.4 V, while the luminanceof each of the red pixel and the green pixel assumed its lowest valuewhen the applied voltage was 7.0 V. When a black display was made byapplication of these voltages, the color coordinates assumed (0.2853,0.3088). Thus, favorable a black display could be realized.

Though the alignment treatment is performed on regions corresponding toall the blue pixels for alignment in a direction that is different fromeach of the alignment directions in regions corresponding to the redpixels and the green pixels, it is possible to subject only a part ofthe regions corresponding to the blue pixels to the alignment treatment.For example, only regions corresponding to blue pixels located around acentral portion of the screen may be subjected to the alignmenttreatment for alignment in a different direction. Usually, the userclosely watches a central portion of a screen with less attention to aperipheral portion apart from the central portion. For this reason, ablack display with decreased bluishness in such a central portion isconsidered to be practically satisfactory.

A variation of this example like the aforementioned variation 1 can berealized. That is, a favorable black display can be obtained by the useof a liquid crystal display of the field sequential system comprising aliquid crystal display element constructed in the same manner as withthe liquid crystal display element according to example 2 except thatany color filter is not provided, and a backlight having LEDs foremitting light of the three primary colors.

Embodiment 3

According to embodiment 3 for carrying out the present invention, thereis provided a liquid crystal display wherein a pretilt angle of liquidcrystal molecules corresponding to blue pixels for a blue display ismade different from each of pretilt angles of liquid crystal moleculescorresponding to red pixels and green pixels for a red display and agreen display, respectively thereby decreasing bluishness when a blackdisplay is made.

EXAMPLE 3

Since the arrangement of a liquid crystal cell included in a liquidcrystal display element of a liquid crystal display according to example3 of this embodiment is similar to that of the liquid crystal cellaccording to example 2 as shown in FIG. 12, description thereof isomitted. Also, other features than the liquid crystal cell are similarto corresponding features of the liquid crystal display element includedin the liquid crystal display according to example 1 having beendescribed with reference to FIG. 1 and, hence, description thereof isomitted.

Hereinafter, the process for manufacturing the liquid crystal displayelement included in the liquid crystal display according to example 3will be described with reference to FIGS. 1 and 12. First, the undersideof transparent electrode 2 and the upper side of transparent electrode 7were each coated with a polyimide alignment film-forming coatingmaterial JALS-614 produced by JSR Co., Ltd. by a spin coating process,which in turn was baked at 180° C. for one hour and then cured to formalignment films 3 and 6.

The alignment films 3 and 6 thus formed were each subjected to a rubbingtreatment using rubbing cloth of rayon. FIG. 14 is an explanatory viewindicating the rubbing direction in this case. As shown in FIG. 14,regions 55R, 55G and 55B of each of the alignment films 3 and 6,respectively, corresponding to red pixels, green pixels and blue pixelswere rubbed in the same direction.

The alignment films 3 and 6 were exposed to ultraviolet light with amask to control amounts of ultraviolet light to be applied to respectiveregions corresponding to red pixels, green pixels and blue pixelsthereby changing their surface conditions. Thereafter, upper substrate102 and lower substrate 103 were bonded to each other so that thespacing therebetween, that is, the thickness of liquid crystal layer 4,assumed 5.4 μm with use of spacers (not shown) produced by SEKISUI FINECHEMICAL Co., Ltd. and a sealing resin named STRUCT BOND 352A producedby MITSUI TOUATSU KAGAKU Co., Ltd. Subsequently, a liquid crystalMT-5583 (refractive index anisotropy Δn=0.140) was injected into theliquid crystal layer 4 by a vacuum injection process to complete theliquid crystal cell 101. The pretilt angles of liquid crystal moleculesat red pixel, green pixel and blue pixel were 5.5 degrees, 5.5 degreesand 0.8 degrees, respectively.

Though the pretilt angles of liquid crystal molecules at respectivepixels can assume values that are not limited to the aforementionedvalues, it becomes impossible to decrease bluishness while keepingfavorable display characteristics if the difference between the pretiltangle of liquid crystal molecules at blue pixels and each of the pretiltangles of liquid crystal molecules at red pixels and at green pixels isnot appropriate. For this reason, the pretilt angle of liquid crystalmolecules at blue pixels should be not less than 5% and not more than50% of each of the pretilt angles of liquid crystal molecules at redpixels and at green pixels, preferably not less than 10% and not morethan 40%.

As shown in FIG. 1, on the upper side of the liquid crystal cell 101thus fabricated were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 a, positive uniaxialretardation film 15 and analyzer 13, and on the underside of the liquidcrystal cell 101 were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 b and polarizer 16, whereby theliquid crystal display element 100 according to example 3 was completed.The aforementioned optical elements were disposed as shown in FIG. 3.

Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 34 nm, which was found from the formula (1) noted above,and retardation Re in the plane of the positive uniaxial retardationfilm 15 was 100 nm, which was found in the same manner. Similarly,retardation Rth in the thicknesswise direction of each of the negativeuniaxial retardation films 12 a and 12 b was 200 nm.

In this example, the retardation Δnd of the liquid crystal layer 4defined by the product of the thickness d of the liquid crystal layer 4and the refractive index anisotropy Δn of liquid crystal molecules 201was set to 0.759 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the liquid crystal display element 100thus manufactured. As a result, the luminance of blue pixels of theliquid crystal display element 100 assumed its lowest value when theapplied voltage was 6.8 V, the luminance of green pixels assumed itslowest value when the applied voltage was 6.9 V, and the luminance ofred pixels assumed its lowest value when the applied voltage was 7.0 V.When a black display was made by application of these voltages to pixelsof respective colors, the color coordinates assumed (0.2978, 0.3013).Thus, a favorable black display could be realized.

As described above, liquid crystal molecules at blue pixels have a lowerpretilt angle than each of the pretilt angles of liquid crystalmolecules at red pixels and at green pixels. For this reason, in anormally white embodiment the voltage-transmittance characteristic ofblue pixels shifts to a higher voltage as compared with the case wherethe pretilt angle of liquid crystal molecules at blue pixels is equal tothose of liquid crystal molecules at red pixels and at green pixels and,hence, the retardation of liquid crystal layer 4 at blue pixels having alower pretilt angle grows larger to assume a value substantially equalto the retardation of the negative retardation film when equal blackdisplay voltages are applied, whereby bluishness that occurs when ablack display is made can be decreased.

A variation of this example like the aforementioned variation 1 can berealized. That is, a favorable black display can be obtained by the useof a liquid crystal display of the field sequential system comprising aliquid crystal display element constructed in the same manner as withthe liquid crystal display element according to example 2 except thatany color filter is not provided, and a backlight having LEDs foremitting light of the three primary colors.

Embodiment 4

According to embodiment 4 for carrying out the present invention, thereis provided a liquid crystal display wherein liquid crystal moleculeshaving a relatively large refractive index anisotropy Δn are employed,while at the same time the retardation Δnd of the liquid crystal layeris made relatively small, whereby bluishness of a black display isdecreased.

EXAMPLE 4

The arrangement of a liquid crystal cell included in a liquid crystaldisplay element of a liquid crystal display according to example 4 ofthis embodiment is similar to that of the liquid crystal cell accordingto example 2 as shown in FIG. 12 and, hence, description thereof isomitted. Also, since other features than the liquid crystal cell aresimilar to corresponding features of the liquid crystal display elementincluded in the liquid crystal display according to example 1 havingbeen described with reference to FIG. 1, description thereof is omitted.

Hereinafter, the process for manufacturing the liquid crystal displayelement 100 included in the liquid crystal display according to example4 will be described with reference to FIGS. 1 and 12. First, theunderside of transparent electrode 2 and the upper side of transparentelectrode 7 were each coated with an alignment film-forming coatingmaterial SE-7492 produced by NISSAN CHEMICAL INDUSTRIES Co., Ltd. by aspin coating process, which in turn was baked at 180° C. for one hourand then cured to form alignment films 3 and 6.

The alignment films 3 and 6 thus formed were rubbed in respectivealignment treatment directions 17 and 18 indicated in FIG. 3.Subsequently, the upper substrate 102 and the lower substrate 103 werebonded to each other so that the spacing therebetween, that is, thethickness of liquid crystal layer 4, assumed 5.0 μm with use of spacers5 produced by SEKISUI FINE CHEMICAL Co., Ltd. and a sealing resin namedSTRUCT BOND 352A produced by MITSUI TOUATSU KAGAKU Co., Ltd. Thereafter,a liquid crystal MJ97206 (refractive index anisotropy Δn=0.160) producedby MERCK CO. was injected into the liquid crystal layer 4 by a vacuuminjection process to complete the liquid crystal cell 101.

As shown in FIG. 1, on the upper side of the liquid crystal cell 101thus fabricated were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 a, positive uniaxialretardation film 15 and analyzer 13, and on the underside of the liquidcrystal cell 101 were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 b and polarizer 16, whereby theliquid crystal display element 100 according to example 3 was completed.The aforementioned optical elements were disposed as shown in FIG. 3.

Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 36 nm, which was found from the formula (1) noted above,and retardation Re in the plane of the positive uniaxial retardationfilm 15 was 150 nm, which was found in the same manner. Retardation Rthin the thicknesswise direction of each of the negative uniaxialretardation films 12 a and 12 b was 220 nm, which was found from theformula (2) noted above.

In this example, the retardation Δnd of the liquid crystal layer 4defined by the product of the thickness d of the liquid crystal layer 4and the refractive index anisotropy Δn of liquid crystal molecules 201was set to 0.80 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the liquid crystal display element 100thus manufactured. As a result, the luminance of blue pixels of theliquid crystal display element 100 assumed its lowest value when theapplied voltage was 6.8 V, the luminance of green pixels assumed itslowest value when the applied voltage was 6.9 V, and the luminance ofred pixels assumed its lowest value when the applied voltage was 7.0 V.When a black display was made by application of these voltages to pixelsof respective colors, the color coordinates assumed (0.2978, 0.3013).Thus, a favorable black display could be realized.

FIG. 15 is a graph for comparison between wavelength dispersioncharacteristics in accordance with retardations of liquid crystal layersusing respective liquid crystal materials that are different inrefractive index anisotropy Δn. In FIG. 15, reference numeral 41indicates the retardation of liquid crystal layer 4 under the conditionsthat: the refractive index anisotropy Δn of the liquid crystal materialis 0.160 and the retardation Δnd is 0.80 μm. Reference numeral 42, onthe other hand, indicates the retardation of the liquid crystal layerunder the conditions that: the refractive index anisotropy Δn of theliquid crystal material is 0.140 (MT-5583) and the retardation Δnd is0.756 μm. As shown in FIG. 15, the wavelength dispersion characteristicof the liquid crystal layer obtained in the case where the refractiveindex anisotropy Δn of the liquid crystal material is larger and theretardation Δnd is smaller, is steeper in a wavelength regioncorresponding to blue. Thus, the wavelength dispersion characteristic inthis case approximates to the wavelength dispersion characteristic inaccordance with retardations of the negative retardation film (see FIG.25) and, hence, bluishness that occurs when a black display is made canbe decreased.

Though it is desirable that the refractive index anisotropy Δn of theliquid crystal material be relatively large while at the same time theretardation Δnd be relatively small, it is practically difficult tospecify a suitable range of each value. In this respect, the inventorsof the present invention provided plural combinations of refractiveindex anisotropy Δn of liquid crystal material and retardation Δnd andconducted experiments to examine to what degree bluishness occurred whena black display was made. The results of the experiments arecollectively shown in FIG. 16.

As shown in FIG. 16, when the refractive index anisotropy Δn of a liquidcrystal material was 0.1431 or less, a black display was found to betinted blue irrespective of the value of retardation Δnd. Likewise, whenthe retardation Δnd was 0.91 or more, a black display was found to betinted blue irrespective of the value of refractive index anisotropy Δnof a liquid crystal material. When the refractive index anisotropy Δn ofa liquid crystal material was 0.1502 or more while at the same time theretardation Δnd was 0.8 μm or less, little bluishness was observed and,hence, a favorable black display could be realized. From these results,it can be judged to be desirable if the refractive index anisotropy Δnof a liquid crystal material is 0.15 or more while at the same time theretardation Δnd is 0.8 μm or less.

A variation of this example like the aforementioned variation 1 can berealized. That is, a favorable black display can be obtained by the useof a liquid crystal display of the field sequential system comprising aliquid crystal display element constructed in the same manner as withthe liquid crystal display element according to example 2 except thatany color filter is not provided, and a backlight having LEDs foremitting lights of the three primary colors.

Embodiment 5

According to embodiment 5 for carrying out the present invention, thereis provided a liquid crystal display wherein refractive indexes nx, nyand nz of a retardation film are all adjusted to 1.5 or less, therebydecreasing bluishness of a black display.

EXAMPLE 5

The arrangement of a liquid crystal cell included in a liquid crystaldisplay element of a liquid crystal display according to example 5 ofthis embodiment is similar to that of the liquid crystal cell accordingto example 2 as shown in FIG. 12 and, hence, description thereof isomitted. Also, since other features than the liquid crystal cell aresimilar to corresponding features of the liquid crystal display elementincluded in the liquid crystal display according to example 1 havingbeen described with reference to FIG. 1, description thereof is omitted.

Hereinafter, the process for manufacturing the liquid crystal displayelement 100 included in the liquid crystal display according to example5 will be described with reference to FIGS. 1 and 12. Upper substrate102 and lower substrate 103 were bonded to each other in the same manneras in example 4, and then a liquid crystal MT-5583 (refractive indexanisotropy Δn=0.140) was injected into liquid crystal layer 4 sandwichedbetween these substrates by a vacuum injection process to completeliquid crystal cell 101.

As shown in FIG. 1, on the upper side of the liquid crystal cell 101thus fabricated were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 a, positive uniaxialretardation film 15 and analyzer 13, and on the underside of the liquidcrystal cell 101 were sequentially stacked negative retardation film 14a, negative uniaxial retardation film 12 b and polarizer 16, whereby theliquid crystal display element 100 according to example 5 was completed.The aforementioned optical elements were disposed as shown in FIG. 3.

The aforementioned negative uniaxial retardation films 12 a and 12 beach comprised a triacetylcellulose (TAC) film and each had aretardation Rth of 175 nm, which was found from the formula (2) notedabove. Further, the refractive indexes nx and ny in the plane of each ofthe negative uniaxial retardation films 12 a and 12 b and the refractiveindex nx in the thicknesswise direction thereof were: nx=1.48671,ny=1.48671, and nz=1.48612.

Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 40 nm, which was found from the formula (1) noted above,and retardation Re in the plane of the positive uniaxial retardationfilm 15 was 150 nm, which was found in the same manner.

In this example, the retardation Δnd of the liquid crystal layer 4defined by the product of the thickness d of the liquid crystal layer 4and the refractive index anisotropy Δn of liquid crystal molecules 201was set to 0.73 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the liquid crystal display element 100thus manufactured. As a result, the luminance of blue pixels of theliquid crystal display element 100 assumed its lowest value when theapplied voltage was 6.0 V, and the luminance of green pixels as well asthe luminance of red pixels assumed its lowest value when the appliedvoltage was 5.6 V. When a black display was made by application of thesevoltages to pixels of respective colors, the color coordinates assumed(0.2878, 0.2995). Thus, a favorable black display could be realized.

Though the refractive indexes nx, ny and nz of each of the negativeuniaxial retardation films 12 a and 12 b each comprising a TAC film were1.48671, 1.48671 and 1.48612, respectively in this example, it isneedless to say that these values are not limitative. Since it isdifficult to procure a film having refractive indexes each assuming avalue less than 1.45 at present, the value which each of the refractiveindexes can assume is desirably not less than about 1.45 and not morethan about 1.5.

Comparative Example 2

The liquid crystal display element included in the liquid crystaldisplay according to example 5 has the negative uniaxial retardationfilms 12 a and 12 b each comprising a TAC film. In contrast, a liquidcrystal display element according to comparative example 2 has negativeuniaxial retardation films 12 a and 12 b each comprising a typicaltriphenylmethane discotic liquid crystal film. Other features of theliquid crystal display element according to comparative example 2 aresimilar to corresponding features of the liquid crystal display elementaccording to example 5 and, hence, description thereof is omitted.

The aforementioned negative uniaxial retardation films 12 a and 12 beach comprising a discotic liquid crystal film each had a retardationRth of 175 nm in the thicknesswise direction thereof, which was foundaccording to the formula (2) noted above. Further, the refractiveindexes nx and ny in the plane of each of the negative uniaxialretardation films 12 a and 12 b and the refractive index nx in thethicknesswise direction thereof were: nx=1.68671, ny=1.68671, andnz=1.68612.

Further, the color coordinates in the direction normal to a blackdisplay made by application of the aforementioned voltages assumed(0.2023, 0.2512), which proved that the black display was tinted blue.

As can be seen from the comparison between example 5 and comparativeexample 2, a difference was observed in bluishness due to a differencein the type of negative uniaxial retardation films 12 a and 12 b.

EXAMPLE 6

The negative uniaxial retardation films included in the liquid crystaldisplay element of the liquid crystal display according to example 5each comprise a TAC film as described above, while in contrast, negativeuniaxial retardation films included in a liquid crystal display elementof a liquid crystal display according to example 6 each comprise a TACfilm and a discotic liquid crystal film.

FIG. 17 is a graph showing wavelength dispersion characteristics inaccordance with retardations of respective optical elements. In FIG. 17,reference numerals 61 and 62 indicate the wavelength dispersioncharacteristic in accordance with retardations of the TAC film and thewavelength dispersion characteristic in accordance with retardations ofthe discotic liquid crystal film, respectively. Reference numerals 63and 64 indicate the wavelength dispersion characteristic in accordancewith retardations of each negative uniaxial retardation film comprisingthe TAC film and the discotic liquid crystal film and the wavelengthdispersion characteristic in accordance with retardations of a liquidcrystal layer, respectively.

As shown in FIG. 17, though the TAC film and the discotic liquid crystalfilm have different wavelength dispersion characteristics in accordancewith retardations, the wavelength dispersion characteristic inaccordance with retardations of each negative uniaxial retardation filmcomprising these films in combination is close to the wavelengthdispersion characteristic in accordance with retardations of the liquidcrystal layer in a wavelength region corresponding to blue. As can beunderstood therefrom, the combination of a TAC film and a discoticliquid crystal film allows easy control of the wavelength dispersioncharacteristic in accordance with retardations of a negative uniaxialretardation film, whereby the wavelength dispersion characteristic ofthe negative uniaxial retardation film can be made substantially conformto the wavelength dispersion characteristic in accordance withretardations of the liquid crystal layer in the wavelength regioncorresponding to blue. As a result, it is possible to decreasebluishness that occurs when a black display is made.

Referring to FIG. 1 as well as FIG. 12, the liquid crystal displayelement included in the liquid crystal display according to example 6has negative uniaxial retardation films 12 a and 12 b each comprising alaminated film in which a TAC film and a discotic liquid crystal filmare stacked on the other. Retardation Re in the plane of each of thenegative uniaxial retardation films 12 a and 12 b was 150 nm, which wasfound from the formula (1) noted above, and retardation Rth in thethicknesswise direction of each of the negative uniaxial retardationfilms was 190 nm, which was found from the formula (2) noted above.Retardation Re in the plane of each of the negative retardation films 14a and 14 b was 40 nm, which was found from the formula (1) noted above.

In this example, the retardation Δnd of the liquid crystal layer 4defined by the product of the thickness d of the liquid crystal layer 4and the refractive index anisotropy Δn of liquid crystal molecules 201was set to 0.73 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the liquid crystal display element 100thus manufactured. As a result, the luminance of blue pixels of theliquid crystal display element 100 assumed its lowest value when theapplied voltage was 5.9 V, the luminance of green pixels assumed itslowest value when the applied voltage was 6.4 V, and the luminance ofred pixels assumed its lowest value when the applied voltage was 6.3 V.When a black display was made by application of these voltages to pixelsof respective colors, the color coordinates assumed (0.3133, 0.3187).Thus, a favorable black display could be realized.

EXAMPLE 7

The liquid crystal display element included in the liquid crystaldisplay according to example 5 having been described with reference toFIG. 1 includes negative retardation films 12 a and 12 b, negativeuniaxial retardation films 14 a and 14 b and positive uniaxialretardation film 15 as retardation films. Stacking plural films as inthis case not only makes the construction complicate but also raises thecost of the liquid crystal display element.

In view of this, a liquid crystal display element included in a liquidcrystal display according to example 7 is constructed to require fewerretardation films. FIG. 18 is a sectional view schematically showing theconstruction of the liquid crystal display element according to example7 of this embodiment. As shown in FIG. 18, the liquid crystal displayelement 100 included in the liquid crystal display according to example7 has liquid crystal cell 101, on the upper side of which aresequentially stacked a negative retardation film 14 a, a biaxialretardation film 71 a and an analyzer 13. On the underside of the liquidcrystal cell 101 are sequentially stacked a negative retardation film 14b, a biaxial retardation film 71 b, and a polarizer 16. The biaxialretardation films 71 a and 71 b are disposed so that their respectiveslow axes extend in directions same as the directions in which thetransmission axes of the analyzer 13 and the polarizer 16 extends.

As apparent from the comparison between FIG. 1 and FIG. 18, the liquidcrystal display element 100 included in the liquid crystal displayaccording to this example does not include any positive uniaxial film 15and does include the biaxial retardation films 71 a and 71 b instead ofnegative uniaxial retardation films 12 a and 12 b. The positive uniaxialfilm 15 is a film required to suppress leakage of light. The liquidcrystal display element 100 according to example 7 is provided with thebiaxial retardation films 71 a and 71 b to realize such suppression oflight leakage.

The biaxial retardation films 71 a and 71 b each comprised a TAC film,and retardation Re in the plane of each of the biaxial retardation films71 a and 71 b was 100 nm, which was found from the formula (1) notedabove, while retardation Rth in the thicknesswise direction thereof was200 nm, which was found from the formula (2) noted above. Retardation Rein the plane of each of the negative retardation films 14 a and 14 b was36 nm, which was found from the formula (1) noted above.

In this example, the retardation Δnd of liquid crystal layer 4 definedby the product of the thickness d of the liquid crystal layer 4 and therefractive index anisotropy Δn of liquid crystal molecules 201 was setto 0.78 μm.

In the same manner as in example 1, an image display was made using theliquid crystal display including the aforementioned liquid crystaldisplay element 100. As a result, the luminance of blue pixels of theliquid crystal display element 100 assumed its lowest value when theapplied voltage was 6.7 V, and the luminance of green pixels as well asthe luminance of red pixels assumed its lowest value when the appliedvoltage was 7.1 V. When a black display was made by application of thesevoltages to pixels of respective colors, the color coordinates assumed(0.2871, 0.2947). Thus, a favorable black display could be realized.

A variation of this example like the aforementioned variation 1 can berealized. That is, a favorable black display can be obtained by the useof a liquid crystal display of the field sequential system comprising aliquid crystal display element constructed in the same manner as withthe liquid crystal display element according to example 2 except thatany color filter is not provided, and a backlight having LEDs foremitting light of the three primary colors.

Embodiment 6

According to embodiment 6 of the present invention, there is provided aliquid crystal display wherein the amounts of light outgoing from thebacklight in respective wavelength regions corresponding to red, greenand blue are substantially equalized, thereby decreasing bluishness thatoccurs when a black display is made.

EXAMPLE 8

FIG. 19 is a sectional view schematically showing the outline of anarrangement of a liquid crystal display according to example 8 of thisembodiment. Liquid crystal display element 100 included in the liquidcrystal display according to this example is similar to the liquidcrystal display element according to example 2 shown in FIG. 12 and,hence, description thereof is omitted by the use of like referencenumerals.

As shown in FIG. 19, backlight 150 disposed below the liquid crystaldisplay element 100 includes a light source 151 comprising a coldcathode ray tube. Between the light source 151 and the liquid crystaldisplay element 100 are disposed interference filters 152. Theinterference filters 152 are each positioned corresponding to theposition of each blue pixel of the liquid crystal display element 100 asshown in FIG. 19.

Such an interference filter 152 is a band pass filter allowing lighthaving a wavelength of 450 nm to pass therethrough. FIG. 20 includesgraphs each showing the spectrum of light outgoing from a light source151; specifically, FIGS. 20( a) and 20(b) are graphs showing spectra,respectively, obtained with and without the provision of theinterference filter 152. As shown in FIG. 20( a), in the case with theprovision of the interference filer 152, the half width of the spectrumof outgoing light in the wavelength region corresponding to blue is 30nm or less. In the case without the provision of the interference filer152, in contrast, the half width assumes a larger value.

Thus, the provision of the interference filter 152 makes it possible todecrease the half width of the spectrum of outgoing light in thewavelength region corresponding to blue and, as a result, makes itpossible to substantially equalize the amounts of outgoing light in thewavelength regions corresponding to red, green and blue, respectively.Hence, bluishness can be decreased when this liquid crystal displaymakes a black display.

EXAMPLE 9

FIG. 21 is a sectional view schematically showing the outline of anarrangement of a liquid crystal display according to example 9 of thisembodiment. Liquid crystal display element 100 included in the liquidcrystal display according to this example is similar to the liquidcrystal display element according to variation 1 shown in FIG. 10 and,hence, description thereof is omitted by the use of like referencenumerals.

As shown in FIG. 21, backlight 150 disposed below the liquid crystaldisplay element 100 includes a light source having LEDs spread withpredetermined intervals for emitting lights of respective three primarycolors. FIG. 22 is a graph showing the emission spectra of LEDs formingthe light source of the aforementioned backlight 150. In the liquidcrystal display according to example 9 the LEDs of the backlight 150emit lights of respective colors by time division in the order of red,green and blue to realize a color display.

When the liquid crystal display of such a field sequential color systemaccording to example 9 made a black display, bluishness could bedecreased.

Meanwhile, it is possible to use an electroluminescent device(hereinafter referred to as “EL”) as a light source included in thebacklight 150 instead of such an LED. FIG. 23 is a graph showingemission spectra of respective Els included in the aforementionedbacklight 150. When a liquid crystal display employing Els as lightsources made a black display in the same manner as above, it was alsopossible to decrease bluishness.

It is needless to say that the aforementioned example 9 may employ LEDsor ELs adapted to emit white light to realize a color display by meansof a color filter system as in example 8.

As described above, any one of the liquid crystal displays according tothe present invention is capable of decreasing bluishness that occurswhen a black display is made.

From the foregoing description, many modifications and other embodimentsof the present invention are apparent for those skilled in the art.Therefore, the foregoing description should be construed as a merelyillustration and is provided for the purpose of teaching the bestembodiment for carrying out the present invention to those skilled inthe art. Specific structures and/or functions of the present inventionmay be modified without departing from the spirit of the presentinvention.

INDUSTRIAL APPLICABILITY

The liquid crystal display according to the present invention is usefulas a wide viewing angle liquid crystal television, a liquid crystalmonitor, and a liquid crystal display of a mobile telephone. The methodof manufacturing a liquid crystal display according to the presentinvention is useful as a method of easily manufacturing such a liquidcrystal display.

1. A liquid crystal display comprising a liquid crystal display elementhaving a liquid crystal layer containing liquid crystal moleculesoriented so as to assume a bend alignment when an image display is beingmade, and at least one negative retardation plate for compensating for aretardation of the liquid crystal layer, wherein the display is made byvarying the retardation of the liquid crystal layer in accordance withvideo signals inputted from outside to vary the transmittance of theliquid crystal display element to light for display, characterized inthat: the negative retardation plate has a hybrid-aligned primary axis,and the liquid crystal display element includes a plurality of redpixels for displaying a red color, a plurality of green pixels fordisplaying a green color, and a plurality of blue pixels for displayinga blue color; and a thickness of the liquid crystal layer associatedwith the blue pixels is larger than a thickness of the liquid crystallayer associated with the red pixels and the green pixels, wherein thethickness of liquid crystal layers associated with red pixels and greenpixels are equal.
 2. The liquid crystal display according to claim 1,wherein a difference between the thickness of the liquid crystal layerassociated with the blue pixels and the thickness of the liquid crystallayer associated with the red pixels and the green pixels is not lessthan 0.2 μm and not more than 1.0 μm.
 3. The liquid crystal displayaccording to claim 1, wherein the thickness of the liquid crystal layerassociated with the blue pixels is not less than 104% and not more than120% of the thickness of the liquid crystal layer associated with thered pixels and the green pixels.
 4. The liquid crystal display accordingto claim 1, further comprising a lighting device having light sourcesfor emitting a red light, a green light and a blue light, respectively,and lighting device control means for controlling the lighting device ina manner to cause the light sources to emit respective color lights bytime division.